Entity Relationship (ER) Diagrams
Esther Sun, Vlada Kim, Tiffany Li, Calvin Ng

Basic Information

Do you have trouble on managing data or arranging information?
If yes, I think you need to learn how to use an Entity Relationship (ER) Diagram.
ER Diagram is a particular graphic that demonstrates how entities are interrelated.
Basically, there are three rules for setting up this type of diagram.
Remember to obey them.

1. No reciting data's columns or data's rows.
2. Every single attribute must be pensile to whole primary key.
3. Every single attribute may ONLY be pensile to primary key.

• Information should not be put in the same table because they usually do not have direct connections.
• Primary key is an unique Identification that can only exist once in each column.

• Content beside primary key is all considered as Foreign Key.
• Give each table a title and primary key should be put at the first row in each column.
• A primary key can never comprise a null value, but a foreign key can hold a null value.
  • Null value ( a non-existing or unlimited value.)

Example

First Normal Form

No reciting data's columns or data's rows



This is the incorrect way of doing the first normal form. As you can see, that the phone # column has more than one phone #. That is not allowed!

Second Normal Form 

Every single attribute must be pensile to whole primary key.

 Third Normal Form

Music Collection Date

First Normal Form

Second Normal Form

Third Normal Form

Video

ETVCdata summary



Summary

An Entity Relationship (ER) diagram is a special graph that shows the relationships between entities in a database. ER diagrams are useing symbols to represent three different types of information. Boxes are usually used to represent entities. Diamonds are normally used to represent relationships and ovals are used to represent attributes.